Add support for running marconi-sidechain as a NixOS module

[koslambrou]

• Added NixOS module in the flake.nix in order to easily run Marconi, Grafana and Prometheus in a NixOS machine.

• Also fixed the start-benchmarking-machine script which was failing following changes to IOGX

• Upgraded IOGX flake following a bug fix related to nixosModules

Pre-submit checklist:

• Branch
  • Tests are provided (if possible)
  • Commit sequence broadly makes sense and have useful messages
  • Important changes are reflected in changelog.d of the affected packages
  • Relevant tickets are mentioned in commit messages
• PR
  • (For external contributions) Corresponding issue exists and is linked in the description
  • Targeting main unless this is a cherry-pick backport
  • Self-reviewed the diff
  • Useful pull request description
  • If relevant, reference the ADR in the PR and reference the PR in the ADR
  • Reviewer requested

[berewt]

@neilmayhew it looks like we didn't look fast enough at this one and we now have merge conflicts to resolve, can you review it?